[apmbench/apmsoak] Allow scaling of load generation with meaningful benchmark results

Using `apm{bench|soak}` in a distributed way to scale load generation would cause the benchmark results to be broken. We should handle this by introducing a mechanism to select a leader/coordinator. The leader will be in charge of collecting and reporting benchmark metrics while the non-leader nodes will generate load and communicate their state to the leader. The communication can be explicit (using a gossip protocol) or implicit (by monitoring benchmark metrics).

Start by locating the apmbench and apmsoak entry points and reading how benchmark metrics are collected and reported. Determine how distributed nodes could select a leader and communicate their state, then define completion as coordinated load generation with the leader producing meaningful aggregate benchmark results.

Written by the indexing model from the issue text.